Conventional fixed, hard memory disk stacks employ clamping arrangements in which one or more hard disks are clamped between a flange at one end of a disk bearing hub and a clamp attached as by screws, to the other end of the disk bearing hub. Such an arrangement, referenced as prior art, appears in FIG. 1 of U.S. Pat. No. 4,945,432, to Matsudaira et al in which the disks are concentrically disposed of the axis of rotation of a disk bearing hub and are axially spaced by spacer rings in a stack between a bottom flange on the hub and a top clamp which is attached to the hub. The application of clamping forces to the top disk of the disk stack, or to a single disk, in the case where only one disk is used, often distorts the plane of the disk(s), resulting in axial displacement of portions of the disk surface which curves the disk surface in a circumferential direction. Clamping forces on the disk also cause disk runout, i.e., radial displacement from concentricity. In a fixed, hard disk stack structure of multiple disks, such disk clamping frequently causes relative circumferential displacement among the disks.
In prior art hard disk stacks of the type described, stresses from mechanical shock and stresses from thermal cycling are also frequent causes of disk displacement relative to the hub and to one another. Stresses at joints between the engaged faces of the disks and hub and the disks and spacer rings, resulting from either mechanical shock or differing thermal dimensional responses, result in slip at the interfaces causing unacceptable misregistration.
While such fixed hard disk stack assemblies have found extensive use in disk drives where, for the storage density, the described displacements were within acceptable limits, they are not usable in smaller drives, or, more generally, in any disk drive of higher track and bit densities, in which misregistration tolerances are less than the described displacements.
The invention described in the patent to Matsudaira et al employs a compliant adhesive or compliant washers or O rings in conjunction with metal spacers for the purpose of mounting glass or ceramic disks in a disk stack. The purpose being to provide an axially yielding, variable disk clamping dimension between the ends of the disk bearing hub, to provide axial compliance in a degree to avoid breaking or loosening of the fragile disks in the presence of varying environmental temperatures. The prior art disk clamping structure for clamping the disk stack between a flange at one end of the disk bearing hub and a clamp at the other end, while also employed by Matsudaira et al to integrate the disk stack and the hub, does not fracture the disks as the clamping dimension changes with changes in temperature, since the compliant washers, O-rings, or adhesive, or combinations thereof, are stated to compress or expand in the degree required to hold disk clamping pressures within acceptable functional limits.
The thrust of the Matsudaira et al disclosure resides in the provision of disk stack structures which have axial compliance. This assembly poses problems, however, since the disk stack, i.e., disks and spacer rings must be unclamped from the hub to be removed for repairs or replacement. This destroys the structural integrity of the memory disk structure. Thus Matsudaira et al, present no teaching of a disk stack structure in which there is no clamping pressure or force on the disks when installed.
Further, in the teaching of Matsudaira et al, there is no thought given to the use of an adhesive as the sole means for attaching the disks to a rotatable body to form an integrated memory disk structure, or of providing such a disk stack structure which is detachable as an assembled unit from a disk spindle or bearing housing.
U.S. Pat. No. 5,031,062 to Joseph A. Wood et al, like Matsudaira et al, employs an adhesive in a disk stack assembly but for a different purpose. Wood et al are concerned with reapplying of the disk surface under clamping pressure and for this reason employs a flowable filler material, preferably an adhesive, which "reduces any differences in the surface topography of the disk and the accompanying clamping-related parts." The adhesive is applied to a spacer ring which spaces the disks on the hub and are stacked on the hub with the spacer therebetween after which clamping pressure is applied by a clamp ring. Here again there is no teaching presented of a disk stack structure in which there is no clamping pressure or force on the disks when installed.
In rigid or hard disk drives in which the disk assembly is provided as a disk cartridge, the cartridge may be inserted and removed from the drive. Such disk cartridge structures, whether employing single or multiple disks, while affording ease of insertion and removal of the disks, lack the overall structural integrity of a fixed hard disk drive and are not functionally adaptable to small form factor disk drives, such as those smaller than the 31/2 inch form factor.
Flexible disks, also known as floppy disks, are provided in protective covers or jackets and are commercially available in single disk packages. Typical structures are described in U.S. Pat. Nos. 4,704,181 (Kubo), U.S. Pat. No. 4,670,803 (DeMoss et al), U.S. Pat. No. 4,794,480 (Jones et al) and U.S. Pat. No. 4,562,505 (Mroz). These are insertable and removable floppy disk structures which function as data storage units in computers and data processors. The jackets have openings for admitting at least a drive spindle to the disk and a read/write head. The undesirable wear of the disks where they are engaged by the spindle, is noted by the patentee Mroz together with prior art attempts to avoid such wear, describing the use of adhesives to attach reinforcing members, mechanical clamps for attaching reinforcing members and the use of microscopic spot welding for reinforcements.
The shortcomings of such prior art approaches are noted. Such shortcomings are said to be overcome by the patented arrangement of Mroz, in which a plastic disk is positioned concentrically between a metallic hub and a metallic ring. The hub and the ring are joined by laser welds which extend between the hub and the rings through the disk.
In all instances such reinforcements are independent of reinforcements on other disks. There is no integration of disks in a disk stack in these assemblies.